Method for producing nickel powder

ABSTRACT

Provided is a method for producing coarse particles of so-called high purity nickel powder containing a small amount of impurities and particularly having a low sulfur content from a nickel ammine sulfate complex solution using fine nickel powder. The method for producing nickel powder from a nickel sulfate solution includes the treatment steps of: (1) a hydroxylation step of producing a precipitate of nickel hydroxide; (2) a complexing step of forming a mixture slurry containing a nickel ammine sulfate complex solution, seed crystals, and the nickel hydroxide; (3) a reduction step of forming a reduced slurry containing the nickel powder formed by precipitation of a nickel component on the seed crystals: and (4) a solid-liquid separation step of subjecting the reduced slurry formed in the reduction step (3) to solid-liquid separation to separately recover the nickel powder and a post-reduction solution.

BACKGROUND Field of the Invention

The present invention relates to a method for obtaining high puritynickel powder having a low sulfur content from a nickel ammine sulfatecomplex solution and briquettes prepared by pressing the powder.

Particularly, the present invention can be applied to the treatment ofan in-process intermediate solution generated from a nickelhydrometallurgical process.

Description of the Related Art

A method for industrially producing nickel powder using ahydrometallurgical process includes a method for producing nickel powderby dissolving a raw material in a sulfuric acid solution followed byremoving impurities to obtain a nickel sulfate solution, adding ammoniato the resulting nickel sulfate solution to form an ammine complex ofnickel, and feeding hydrogen gas into the produced nickel ammine sulfatecomplex solution to reduce nickel.

For example, POWDER METALLURGY, 1958, No. 1/2, pp. 40-52 describes aprocess for producing nickel powder by adding an iron compound as seedcrystals during the reduction reaction to precipitate nickel on the ironcompound, but the process is problematic in that iron derived from theseed crystals is mixed into the product.

Further, a method for obtaining nickel powder using a reducing agentother than hydrogen gas has also been proposed.

For example, Japanese Patent Laid-Open No. 2005-240164 discloses nickelpowder which is inexpensive, is excellent in weatherability, has lowelectric resistance in a state where it is kneaded with a resin, reducesinitial electric resistance and electric resistance in use, can bestably used over a long period of time, and is suitable as conductiveparticles for a conductive paste and a conductive resin, and a methodfor producing the same.

The nickel powder disclosed in Japanese Patent Laid-Open No. 2005-240164contains 1 to 20% by mass of cobalt with the balance consisting ofnickel and unavoidable impurities, includes secondary particles in whichprimary particles are aggregated, and has an oxygen content of 0.8% bymass or less. Cobalt is contained only in the surface layer part of thesecondary particles, and it is said that the cobalt content in thesurface layer part is preferably 1 to 40% by mass. When the nickelpowder is intended to be obtained by the disclosed production method,cobalt will coexist. Therefore, the method is not suitable for anapplication in which nickel and cobalt are present in combination, forexample, in a nickel oxide ore; these metals are separated; and eachmetal is intended to be economically recovered as high purity metal.

Further, Japanese Patent Laid-Open No. 2010-242143 provides a method forproducing metal powder by a liquid phase reduction method that isimproved so that a particle aggregate may be hardly produced.

The method for producing metal powder includes a first step ofdissolving a metal compound, a reducing agent, a complexing agent, and adispersant to prepare an aqueous solution containing metal ions derivedfrom the metal compound and a second step of adjusting the pH of theaqueous solution to reduce the metal ions with the reducing agent toprecipitate the metal powder.

However, this production method requires high cost since an expensivechemical is used, and is not economically advantageous for applying themethod to a process operated on a large scale as the above nickelsmelting.

Although various processes for producing nickel powder have beenproposed as described above, a method for producing high purity nickelpowder using industrially inexpensive hydrogen gas has not beenproposed.

In these circumstances, the present invention intends to provide amethod for producing coarse particles of so-called high purity nickelpowder containing a smaller amount of impurities and particularly havinga low sulfur content from a nickel ammine sulfate complex solution usingindustrially inexpensive hydrogen gas and using fine nickel powder.

SUMMARY

The first aspect of the present invention to solve the above problem isa method for producing nickel powder containing a small amount ofimpurities from a nickel sulfate solution containing the impurities,including the following process steps (1) to (4):

-   (1) a hydroxylation step of adding an alkali to the nickel sulfate    solution containing the impurities to produce a precipitate of    nickel hydroxide having a decreased concentration of the impurities    contained therein;-   (2) a complexing step of adding a post-reduction solution obtained    in a solid-liquid separation step (4) and nickel powder as seed    crystals to the precipitate of nickel hydroxide having the decreased    concentration of the impurities contained therein and produced in    the hydroxylation step (1), and dissolving the precipitate of nickel    hydroxide, to form a mixture slurry containing a nickel ammine    sulfate complex solution, seed crystals, nickel hydroxide and the    impurities contained in the precipitate of nickel hydroxide;-   (3) a reduction step of blowing hydrogen gas into the mixture slurry    formed in the complexing step (2) to form a reduced slurry    containing nickel powder formed by precipitation of a nickel    component in the mixture slurry on the seed crystals; and-   (4) the solid-liquid separation step of subjecting the reduced    slurry formed in the reduction step (3) to solid-liquid separation    to separately recover the nickel powder and a post-reduction    solution, repeatedly sieving the recovered nickel powder by particle    size and subjecting a nickel powder having particles smaller than a    predetermined size as seed crystals to either or both of the    complexing step (2) and the reduction step (3), and repeatedly    subjecting the recovered post-reduction solution to the complexing    step (2).

The second aspect of the present invention is a method for producingnickel powder according to the first aspect, wherein repeated operationof sieving the nickel powder recovered in the solid-liquid separationstep (4) by particle size, and adding a nickel powder having particlessmaller than a predetermined size as seed crystals to either or both ofthe complexing step (2) and the reduction step (3) provides a nickelpowder coarser than the nickel powder of seed crystals.

The third aspect of the present invention is a method for producingnickel powder according to the second aspect, wherein seed crystals tobe added to either or both of the complexing step (2) and the reductionstep (3) have an average particle size of 0.1 to 100 μm.

The fourth aspect of the present invention is a method for producingnickel powder according to the first to the third aspects, wherein, inthe complexing step (2), when the mixture slurry containing the nickelammine sulfate complex solution, the seed crystals, and nickel hydroxideis formed, a dispersant is further added to the mixture slurry.

The fifth aspect of the present invention is a method for producingnickel powder according to the first to the fourth aspects, wherein, inthe complexing step (2), the amount of the seed crystals added is 1 to100% based on the weight of nickel in the nickel ammine sulfate complexsolution.

The sixth aspect of the present invention is a method for producingnickel powder according to the first to the fifth aspects, wherein thereduced slurry is sieved, and the undersize nickel powder and theundersize reduced slurry of the resulting post-reduction solution arerepeatedly used as parts of the nickel powder as seed crystals and thepost-reduction solution in the complexing step (2).

The seventh aspect of the present invention is a method for producingnickel powder according to the sixth aspect, wherein the complexing step(2) is composed of two steps: a dissolution step of adding thepost-reduction solution to obtain the nickel ammine sulfate complexsolution: and a seed crystal addition step of adding the mixture slurrycontaining either nickel powder or nickel powder and the post-reductionsolution.

The eighth aspect of the present invention is a method for producingnickel powder according to the first aspect, wherein the nickel sulfatesolution is obtained by dissolving, in a sulfuric acid solution, atleast one of nickel and cobalt mixed sulfide, nickel sulfide, coarsenickel sulfate, nickel oxide, nickel hydroxide, nickel carbonate, andmetallic nickel powder which is recovered by leaching a nickel oxideore.

The ninth aspect of the present invention is a method for producingnickel powder according to the first aspect, wherein the nickel sulfatesolution is obtained by: a leaching step of dissolving anickel-containing material having cobalt as an impurity; and a solventextraction step of adjusting pH of the leachate containing nickel andcobalt obtained in the leaching step and then separating the leachateinto a nickel sulfate solution and a cobalt-recovering solution bysolvent extraction.

A tenth aspect of the present invention is a method for producing nickelpowder according to the first aspect, wherein the concentration ofammonium sulfate in the nickel ammine sulfate complex solution is 100 to500 g/L, and the ammonium concentration is 1.9 or more in a molar ratiobased on the nickel concentration in the nickel ammine sulfate complexsolution.

The eleventh aspect of the present invention is a method for producingnickel powder according to the first aspect, wherein in the reductionstep (3) hydrogen gas is blown while maintaining the temperature in therange of 100 to 200° C. and the pressure in the range of 0.8 to 4.0 MPa.

The twelfth aspect of the present invention is a method for producingnickel powder according to the fourth aspect, wherein the dispersantcontains a polyacrylate salt.

A thirteenth aspect of the present invention is a method for producingnickel powder according to the first aspect, including: a nickel powderbriquetting step of processing the nickel powder obtained in thereduction step (3) into nickel briquettes in a block form using abriquetting machine; and a briquette sintering step of subjecting theresulting nickel briquettes in the block form to sintering treatmentunder holding conditions at a temperature of 500 to 1200° C. in ahydrogen atmosphere to form nickel briquettes as a sintered compact.

The fourteenth aspect of the present invention is a method for producingnickel powder according to the first aspect, including an ammoniumsulfate recovery step of concentrating the post-reduction solution fromthe solid-liquid separation step (4) to crystallize ammonium sulfate andrecovering ammonium sulfate crystals.

The fifteenth aspect of the present invention is a method for producingnickel powder according to the first aspect, including an ammoniarecovery step of adding an alkali to the post-reduction solution fromthe solid-liquid separation step (4), heating the resulting mixture tovolatilize ammonia gas and recovering the ammonia gas.

Advantageous Effect of Invention

According to the present invention, in a method for producing nickelpowder using hydrogen gas from a nickel ammine sulfate complex solution,high purity nickel powder containing a smaller amount of impurities canbe easily obtained and an industrially remarkable effect can be thusachieved.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a production flow chart of nickel powder according to thepresent invention.

DETAILED DESCRIPTION

The present invention is characterized in that high purity nickel powdercontaining a smaller amount of impurities is produced from a nickelammine sulfate complex solution by subjecting a process solution of thehydrometallurgical process to steps (1) to (4) as shown below, in themethod for obtaining nickel powder from a nickel ammine sulfate complexsolution.

Hereinafter, the method for producing high purity nickel powderaccording to the present invention will be described with reference tothe production flow chart of high purity nickel powder according to thepresent invention shown in FIG. 1.

[Leaching Step]

First, the leaching step is a step of dissolving a nickel-containingmaterial, serving as a starting material, such as an industrialintermediate including one or a mixture of two or more selected fromnickel and cobalt mixed sulfide, crude nickel sulfate, nickel oxide,nickel hydroxide, nickel carbonate, nickel powder, and the like withsulfuric acid to leach nickel to produce a leachate (sulfuric acidsolution containing nickel), and is performed by a known method, forexample, disclosed in Japanese Patent Laid-Open No. 2005-350766.

[Solvent Extraction Step]

Next, the pH of the leachate is adjusted, and the resulting leachate issubjected to the solvent extraction step.

This step is a step of bringing an organic phase into contact with theleachate, which is obtained in the leaching step and then subjected topH adjustment, to exchange the components in each phase, therebyincreasing the concentration of some components and reducing theconcentration of other different components in an aqueous phase.

In the present invention, 2-ethylhexylphosphonic acid mono-2-ethylhexylester or di-(2,4,4-trimethylpentyl)phosphinic acid is used as theorganic phase to selectively extract impurity elements, particularlycobalt, in the leachate as a cobalt recovering solution to obtain anickel sulfate solution having a low cobalt concentration.

In addition, aqueous ammonia produced in the ammonia recovery step to bedescribed below can be also used as the aqueous ammonia used for pHadjustment during this step.

(1) Hydroxylation Step

In the present invention, an alkali is added to a nickel sulfatesolution obtained through the above steps to produce a precipitate ofnickel hydroxide, thereby separating a precipitate of the solidcomponent from the liquid component.

As a result of this treatment, most impurities contained in nickelsulfate are separated into the liquid component, so that theconcentration of impurities contained in the precipitate of nickelhydroxide as the solid component can be decreased.

As an alkali to be added here, sodium hydroxide, calcium hydroxide, orthe like that can be industrially inexpensively obtained in largeamounts is preferably used.

(2) Complexing Step

The complexing step is composed of two steps, specifically a dissolutionstep and a seed crystal addition step, wherein first, in the dissolutionstep, ammonia in the form of a post-reduction solution obtained bysubjecting the reduced slurry obtained in the reduction step (3) tosolid-liquid separation is added to the precipitate of nickel hydroxideobtained in the hydroxylation step (1), so as to form a mixed solutionof nickel hydroxide and the post-reduction solution, thereby complexingtreatment is performed to produce a nickel ammine sulfate complex whichis an ammine complex of nickel, and thus a nickel ammine sulfate complexsolution thereof is formed.

At this time, the ammonium concentration can be adjusted by addingammonia gas or aqueous ammonia. The ammonia is added so that theammonium concentration at that time may be 1.9 or more in a molar ratiobased on the concentration of nickel in the solution. If the ammoniumconcentration of the ammonia to be added is less than 1.9, nickel willnot form an ammine complex, but a precipitate of nickel hydroxide willbe produced.

Further, in order to adjust the concentration of ammonium sulfate,ammonium sulfate can be added in this step.

The concentration of ammonium sulfate at this time is preferably 100 to500 g/L. If the concentration is more than 500 g/L, solubility will beexceeded to precipitate crystals, and it is difficult to achieve aconcentration of less than 100 g/L in terms of the metal balance in theprocess.

Further, the ammonia gas or aqueous ammonia produced in the ammoniarecovery step to be described below can be also used as the ammonia gasor aqueous ammonia used in this step.

Subsequent to the dissolution step, a seed crystal addition step isperformed by adding the nickel powder having an average particle size of0.1 to 5 μm as seed crystals in the form of a nickel powder slurry tothe produced nickel ammine sulfate complex solution, so as to form amixture slurry containing the seed crystals, the nickel ammine sulfatecomplex solution, and nickel hydroxide.

The weight of the seed crystals added at this time is preferably 1 to100% based on the weight of nickel in the nickel ammine sulfate complexsolution. If the weight of the seed crystals is less than 1%, thereaction efficiency during the reduction in the next step will besignificantly reduced. Further, if the weight of the seed crystals ismore than 100%, the amount of the seed crystals used will be a largeamount, which requires much cost for producing seed crystals and is noteconomical.

Further, a dispersant may be added at the same time. Since the seedcrystals are dispersed by adding the dispersant, the efficiency of thesubsequent reduction step can be increased.

The dispersant used here is not particularly limited as long as it has asulfonate, but a lignosulfonate is preferred as a dispersant that can beindustrially inexpensively obtained.

(3) Reduction Step

The reduction step is a step of forming a reduced slurry containingnickel powder that is formed by blowing hydrogen gas into the obtainedmixture slurry to reduce and precipitate a nickel component in thesolution on the seed crystals.

At this time, reaction temperature is preferably 100 to 200° C. If thetemperature is lower than 100° C., and more preferably lower than 150°C., reduction efficiency will be reduced, and even if the temperature ishigher than 200° C., there will be no influence on the reaction, and theloss of thermal energy and the like will increase.

Further, the pressure during the reaction is preferably 0.8 to 4.0 MPa.If the pressure is less than 0.8 MPa, reaction efficiency will bereduced, and even if the pressure exceeds 4.0 MPa, there will be noinfluence on the reaction, and the loss of hydrogen gas will increase.

In the liquid of the resulting mixture slurry, magnesium ions, sodiumions, calcium ions, sulfate ions, and ammonium ions are mainly presentas impurities, but since all the ions remain in the solution, highpurity nickel powder can be produced.

Further, nickel hydroxide in the liquid of the mixture slurry reactswith ammonium ions produced by reduction reaction, is dissolved as anickel ammine complex in the solution, reacts with hydrogen gas, and isthus reduced, so that nickel is precipitated on the seed crystals.

(4) Solid-Liquid Separation Step

The reduced slurry produced in the previous reduction step (3) issubjected to solid-liquid separation, thereby separately recovering highpurity nickel powder containing a small amount of impurities and apost-reduction solution. The high purity nickel powder is repeatedly fedto either or both of the complexing step (2) as seed crystals and thereduction step (3) as nickel powder to be subjected to particle growth.

Meanwhile, in this step, the recovered post-reduction solution isrepeatedly used as a substitute for aqueous ammonia in the complexingstep (2).

Specifically, the recovered high purity nickel powder containing a smallamount of impurities and having a small size or the same pulverized tohave a smaller size is repeatedly fed as seed crystals to the complexingstep (2). The nickel powder is further added to a nickel ammine sulfatecomplex solution obtained in the complexing step (2). Hydrogen gas isthen fed in the reduction step (3) to reduce and precipitate nickel onthe high purity nickel powder, so as to be able to grow particles.

Further, by repeating the feeding to the reduction step for a pluralityof times, high purity nickel powder having higher bulk density and alarger particle size can be produced.

Further, the resulting high purity nickel powder may be finished intothe shape of briquettes that are coarser, not easily oxidized, andeasily handled through the nickel powder briquetting step and briquettefiring step as described below.

Furthermore, an ammonia recovery step may be provided.

[Nickel Powder Briquetting Step]

The high purity nickel powder produced by the present invention is driedand then processed for shaping with a briquetting machine or the like toobtain nickel briquettes in a block form as a product form.

Further, in order to improve the processability to form the briquettes,a material that does not impair the product quality such as water may beadded as a binder to the nickel powder depending on the case.

[Briquette Sintering Step]

The nickel briquettes prepared in the briquetting step is subjected toroasting and sintering in a hydrogen atmosphere to prepare a briquettesintered compact. This treatment is performed for increasing thestrength and removing ammonia and a sulfur component remaining in a verysmall amount, and the roasting and sintering temperature of thetreatment is preferably 500 to 1200° C. If the temperature is lower than500° C., the sintering will be insufficient, and even if the temperatureexceeds 1200° C., the efficiency will hardly change but the loss ofenergy will increase.

[Ammonium Sulfate Recovery Step]

The post-reduction solution produced by the solid-liquid separation step(4), in which the nickel powder is separated as a solid phase, after thereduction step (3) contains ammonium sulfate and ammonia.

Thus, the ammonium sulfate can be recovered as ammonium sulfate crystalsby subjecting the post-reduction solution to the ammonium sulfaterecovery step, in which the post-reaction solution is heated andconcentrated to precipitate ammonium sulfate.

[Ammonia Recovery Step]

Further, ammonia can be recovered by adding an alkali to thepost-reduction solution to adjust the pH to 10 to 13 and then heatingthe resulting solution to volatilize ammonia gas.

The alkali used here suitably includes, but is not limited to, causticsoda and slaked lime, because they are industrially inexpensive.

Further, the recovered ammonia gas can produce aqueous ammonia bybringing it into contact with water, and the resulting aqueous ammoniacan be repeatedly used in the process.

EXAMPLES

The present invention will be described below in more detail usingExamples.

Example 1

To 1000 ml of a nickel sulfate solution with a nickel concentration of120 g/L, was added 800 ml of slaked lime adjusted to have a slurryconcentration of 200 g/L, so as to obtain 116 g of nickel hydroxide.

The nickel hydroxide was added together with 12.8 g of nickel powderhaving an average particle size of 2 μm as seed crystals to 1700 ml of amixture of a nickel sulfate solution having a nickel concentration of 30g/L and an ammonium sulfate solution having an ammonia concentration of40 g/L, and then the mixture was stirred to prepare a mixture slurry.

The mixture slurry was heated to 185° C. in an autoclave with stirring,and hydrogen gas was blown and fed into the slurry so that the pressurein the autoclave became 3.5 MPa to subject the mixture slurry to thereduction step. The reduced slurry was subjected to the solid-liquidseparation step by filtration to recover nickel powder having grownparticles.

At this time, the recovered nickel powder had an average particle sizeof 65 μm and the amount of the nickel powder recovered was 119 g.

Further, the recovered nickel powder was washed with pure water and thenanalyzed for the impurity content in the nickel powder.

The results are shown in Table 1. The mixing of Mg and Na into thenickel powder was not observed, and high purity Ni powder was able to beproduced.

TABLE 1 Ni Mg Na Example 1 — <0.005% <0.005%

Example 2

To 1000 ml of a nickel sulfate solution having a nickel concentration of120 g/L, was added 800 ml of slaked lime adjusted to have a slurryconcentration of 200 g/L, to obtain 116 g of nickel hydroxide.

The 116 g of nickel hydroxide was mixed with a nickel ammine sulfatesolution having a nickel concentration of 30 g/L, 232 ml of 25% aqueousammonia and 225 g of ammonium sulfate, and then pure water was added tothe mixture to prepare 1000 ml of a solution. 20 g of nickel powderhaving an average particle size of 1 μm was added as seed crystals tothe solution, to prepare a mixture slurry.

Next, the prepared mixture slurry was heated to 120° C. with stirring inan autoclave, and hydrogen gas was blown and fed into the slurry so thatthe pressure in the autoclave became 3.5 MPa to subject the slurry tonickel powder production treatment which is reduction treatment.

After the lapse of one hour from the start of feeding hydrogen gas, thefeed of hydrogen gas was stopped, and the autoclave was cooled. Areduced slurry obtained after cooling was subjected to solid-liquidseparation by filtration to recover high purity nickel powder having asmall size. The nickel powder recovered at this time was 70 g.

Next, 116 g of nickel hydroxide was added to the post-reduction solutionafter the above solid-liquid separation, so as to prepare a slurry. Tothe slurry, was added the entire amount of the recovered high puritynickel powder having a small size to prepare a mixture slurry.

The mixture slurry was heated to 120° C. with stirring in an autoclave,and hydrogen gas was blown and fed into the slurry so that the pressurein the autoclave became 3.5 MPa.

After the lapse of one hour from the start of feeding hydrogen gas, thefeed of hydrogen gas was stopped, and the autoclave was cooled. A slurryobtained after cooling was subjected to solid-liquid separation byfiltration to recover high purity nickel powder having grown particles.

Example 3

The post-reduction solution obtained in the solid-liquid separation stepof Example 1 was used for a part of an ammonia source to prepare amixture slurry. The slurry was subjected to the reduction step under thesame conditions as those in Example 1, and then subjected to thesolid-liquid separation step, so as to recover nickel powder havinggrown particles. Nickel powder similar to that in Example 1 wasrecovered.

Example 4

To a solution containing the nickel powder prepared under the sameconditions as in Example 1, 336 g of nickel sulfate and 330 g ofammonium sulfate, was added 191 ml of 25% aqueous ammonia, and the totalvolume of the mixture was adjusted to 1000 ml. The resultant wassubjected again to the reduction step and the solid-liquid separationstep under the same conditions as in Example 1 to prepare nickel powderhaving grown particles. This operation was repeated 10 times using theprepared nickel powder to further grow particles of the nickel powder.

The recovered nickel powder had an average particle size of 111 μm, suchthat the particle size grew to a size 1.7 times the size of the nickelpowder of Example 1.

The nickel powder obtained by the repeated operation had a sulfurcontent of 0.04%. Sodium and magnesium were at a minimum limit ofdetermination or lower levels similar to Table 1 above.

Then, the obtained nickel powder was heated to 1000° C. in a 2% hydrogenatmosphere and held for 60 minutes. Nickel powder obtained after theholding had a sulfur content of 0.008%, and the sulfur content could befurther reduced by roasting.

Example 5

To 1000 ml of a nickel ammine sulfate complex solution shown in Table 2,was added 75 g of nickel powder having an average particle size of 1 μmas seed crystals. Then, the resulting mixture was heated to 185° C. withstirring in an autoclave, and hydrogen gas was blown and fed into themixture so that the pressure in the autoclave became 3.5 MPa.

After the lapse of one hour from the start of feeding hydrogen gas, thefeed of hydrogen gas was stopped, and the autoclave was cooled. A slurryobtained after cooling was subjected to solid-liquid separation byfiltration to recover nickel powder, which was washed with pure waterand then analyzed for the impurity content in the nickel powder.

The results are shown in Table 2.

The mixing of Mg and Na into the nickel powder was not observed, andhigh purity Ni powder was able to be produced.

TABLE 2 Ni Mg Na Nickel ammine sulfate 75 0.1 7.0 complex solution [g/L][g/L] [g/L] High purity nickel — <0.005% <0.005% powder

Example 6

To a nickel ammine sulfate solution prepared by mixing 135 g of nickelsulfate hexahydrate, 191 ml of 25% aqueous ammonia, 169 g of ammoniumsulfate and pure water, was added 75 g of nickel hydroxide. Pure waterwas added thereto so that the total volume of the solution was adjustedto 1000 ml. 15 g of nickel powder having an average particle size of 1μm was added as seed crystals, to prepare a mixture slurry.

The mixture slurry was heated to 100° C. with stirring in an autoclave,and hydrogen gas was fed into the mixture slurry so that the pressure inthe autoclave became 3.5 MPa to subject the slurry to nickel powderproduction treatment.

After the lapse of one hour from the start of feeding hydrogen gas, thefeed of hydrogen gas was stopped, and the autoclave was cooled. Areduced slurry obtained after cooling was subjected to solid-liquidseparation by filtration to recover high purity nickel powder having asmall size. The rate of nickel reduction was 58%.

Example 7

With the use of the same mixture slurry as in Example 6, the sameoperation as in Example 6 was performed under conditions of thetemperature of 100° C., and the pressure within an autoclave of 0.8 MPa.The resulting rate of nickel reduction was 56%.

Example 8

With the use of the same mixture slurry as in Example 6, the sameoperation as in Example 6 was performed under conditions of thetemperature of 120° C., and the pressure within an autoclave of 3.5 MPa.The resulting rate of nickel reduction was 74%.

Example 9

With the use of the same mixture slurry as in Example 6, the sameoperation as in Example 6 was performed under conditions of thetemperature of 120° C., and the pressure within an autoclave of 2.0 MPa.The resulting rate of nickel reduction was 74%.

Example 10

With the use of the same mixture slurry as in Example 6, the sameoperation as in Example 6 was performed under conditions of thetemperature of 120° C., and the pressure within an autoclave of 1.5 MPa.The resulting rate of nickel reduction was 74%.

As understood from the results of Examples 6 to 10 shown in Table 3,high purity nickel was produced in all examples, and the rates ofreduction were not significantly affected by pressure and weresignificantly decreased due to decreases in temperature.

TABLE 3 Temperature Pressure Rate of Ni reduction [° C.] [MPa] [%]Example 6 100 3.5 58 Example 7 100 0.8 56 Example 8 120 3.5 74 Example 9120 2.0 74 Example 10 120 1.5 74

Comparative Example 1

Nickel powder was prepared under the same conditions as in Example 1except that the hydroxylation step in Example 1 was not performed, 191ml of 25% aqueous ammonia was added to a nickel sulfate solutioncontaining 75 g of nickel and, a solution containing 330 g of ammoniumsulfate, the solution was adjusted to have a total volume of 1000 ml,and then to the solution was added 7.5 g of nickel powder having anaverage particle size of 1 μm as seed crystals, so as to prepare amixture slurry.

The recovered nickel powder was washed with pure water and then analyzedfor the impurity content in the nickel powder.

The results are shown in Table 4. The mixing of Mg and Na into thenickel powder was at levels higher than those in Example 1. In addition,an average particle size and the amount of the nickel powder recoveredwere almost equivalent to those in Example 1.

TABLE 4 Ni Mg Na Comparative — 0.02% 0.02% example 1

Comparative Example 2

With the use of the same method as in the above Comparative Example 1,nickel powder was prepared without performing the hydroxylation step.The nickel powder was repeatedly subjected to the same method as in theabove Example 3 for 10 times, to grow particles. The sulfur content inthe nickel powder obtained by the repeated operation was 0.1%. Hence,high purity nickel powder equivalent to that having a sulfur content of0.04% obtained in Example 3 of the present invention could not beobtained.

1. A method of producing nickel powder containing a small amount ofimpurities from a nickel sulfate solution containing the impurities,comprising the process steps of: (1) a hydroxylation step of adding analkali to the nickel sulfate solution containing the impurities toproduce a precipitate of nickel hydroxide having a decreasedconcentration of the impurities contained therein; (2) a complexing stepof adding a post-reduction solution obtained in a solid-liquidseparation step (4) and nickel powder as seed crystals to theprecipitate of nickel hydroxide having the decreased concentration ofthe impurities contained therein and produced in the hydroxylation step(1), and dissolving the precipitate of nickel hydroxide, to form amixture slurry containing a nickel ammine sulfate complex solution, seedcrystals, nickel hydroxide and the impurities contained in theprecipitate of nickel hydroxide; (3) a reduction step of blowinghydrogen gas into the mixture slurry formed in the complexing step (2)to form a reduced slurry containing nickel powder formed byprecipitation of a nickel component in the mixture slurry on the seedcrystals; and (4) a solid-liquid separation step of subjecting thereduced slurry formed in the reduction step (3) to solid-liquidseparation to separately recover the nickel powder and a post-reductionsolution, repeatedly sieving the recovered nickel powder by particlesize and subjecting a nickel powder having particles smaller than apredetermined size as seed crystals to either or both of the complexingstep (2) and the reduction step (3), and, repeatedly subjecting therecovered post-reduction solution to the complexing step (2).
 2. Themethod of producing nickel powder according to claim 1, wherein repeatedoperation of sieving the nickel powder recovered in the solid-liquidseparation step (4) by particle size, and adding a nickel powder havingparticles smaller than a predetermined size as seed crystals to eitheror both of the complexing step (2) and the reduction step (3) provides anickel powder coarser than the nickel powder of seed crystals.
 3. Themethod of producing nickel powder according to claim 2, wherein seedcrystals to be added to either or both of the complexing step (2) andthe reduction step (3) have an average particle size of 0.1 to 100 μm.4. The method of producing nickel powder according to claim 1, wherein,in the complexing step (2), when the mixture slurry containing thenickel ammine sulfate complex solution, the seed crystals, and nickelhydroxide is formed, a dispersant is further added to the mixtureslurry.
 5. The method of producing nickel powder according to claim 1,wherein, in the complexing step (2), an amount of the seed crystalsadded is 1 to 100% based on the weight of nickel in the nickel amminesulfate complex solution.
 6. The method of producing nickel powderaccording to claim 1, wherein the reduced slurry is sieved, andundersize nickel powder and undersize reduced slurry of the resultingpost-reduction solution are repeatedly used as parts of the nickelpowder as seed crystals and the post-reduction solution in thecomplexing step (2).
 7. The method of producing nickel powder accordingto claim 6, wherein the complexing step (2) is composed of two steps: adissolution step of adding the post-reduction solution to obtain thenickel ammine sulfate complex solution; and a seed crystal addition stepof adding the mixture slurry containing either nickel powder or nickelpowder and the post-reduction solution.
 8. The method of producingnickel powder according to claim 1, wherein the nickel sulfate solutionis obtained by dissolving, in a sulfuric acid solution, at least one ofnickel and cobalt mixed sulfide, nickel sulfide, crude nickel sulfate,nickel oxide, nickel hydroxide, nickel carbonate, and metallic nickelpowder which is recovered by leaching a nickel oxide ore.
 9. The methodof producing nickel powder according to claim 1, wherein the nickelsulfate solution is obtained by: a leaching step of dissolving anickel-containing material having cobalt as an impurity; and a solventextraction step of adjusting pH of the leachate containing nickel andcobalt obtained in the leaching step and then separating the leachateinto a nickel sulfate solution and a cobalt-recovering solution bysolvent extraction.
 10. The method of producing nickel powder accordingto claim 1, wherein a concentration of ammonium sulfate in the nickelammine sulfate complex solution is 100 to 500 g/L, and an ammoniumconcentration is 1.9 or more in a molar ratio based on a nickelconcentration in the nickel ammine sulfate complex solution.
 11. Themethod of producing nickel powder according to claim 1, wherein, in thereduction step (3), hydrogen gas is blown while maintaining thetemperature in the range of 100 to 200° C. and the pressure in the rangeof 0.8 to 4.0 MPa.
 12. The method of producing nickel powder accordingto claim 4, wherein the dispersant contains a polyacrylate salt.
 13. Themethod of producing nickel powder according to claim 1, comprising: anickel powder briquetting step of processing the nickel powder obtainedin the reduction step (3) into nickel briquettes in a block form using abriquetting machine; and a briquette sintering step of subjecting theresulting nickel briquettes in the block form to sintering treatmentunder holding conditions at a temperature of 500 to 1200° C. in ahydrogen atmosphere to form nickel briquettes as a sintered compact. 14.The method of producing nickel powder according to claim 1, comprisingan ammonium sulfate recovery step of concentrating the post-reductionsolution from the solid-liquid separation step (4) to crystallizeammonium sulfate and recovering ammonium sulfate crystals.
 15. Themethod of producing nickel powder according to claim 1, comprising anammonia recovery step of adding an alkali to the post-reduction solutionfrom the solid-liquid separation step (4), heating the resulting mixtureto volatilize ammonia gas and recovering the ammonia gas.